Herpes simplex virus [HSV] isolate HSV-1 (17) is neuroviorulent following corneal infection of young adult mice because the virus has the capacity to spread to the trigeminal ganglion and brain from sites of infection. HSV-2 (186) isolate however, is not neurovirulent following corneal inoculation because the virus is 1000-fold less efficient in reaching the trigeminal gaglion and brain from the cornea. We have found that an interpic recombinant designated B1E, which possesses 60 kb of HSV-1 (17) DNA from map units 0.3 to 0.65 and two 45 kb stretches of 186 DNA from map units 0 to 0.3 and map units 0.65 to 1.0 has inherited the neurovirulent phenotype of the HSV-1 (17) parent because B1E spreads from infected corneas into the trigeminal ganglion and brain. The goal of this study, therefore, is to identify the gene or genes inherited from the HSV-1 (17) parent which are responsible for ingression of B1E into the trigeminal ganglion from the cornea. In order to localize the neurovirulent genes within the B1E recombinant to the right, middle or left regions of the 60 kb HSV-1 (17) insert, 3 genetic crosses will be performed by mixed infection of cells with HSV-1 (17) and HSV-2 (186). The cross HSV-1 tsJ X HSV-2 (186) will be used to produce intertypic recombinants with HSV-1 (17) DNA from map units 0.3 to 0.5 and HSV-2 (186) DNA from map units 0 to 0.3 and 0.5 to 1.0. Cross B1E X 186 [PAA-R,ts] will be used to generate recombinants with HSV-1 (17) DNA from map unit 0.5 to 0.65 and HSV-2 (186) DNA from map units 0 to 0.5 and 0.65 to 1.0 while the cross HSV-1 (17) X HSV-2 (186) (ts-, PAA-R) will yield recombinants with HSV-2 (186) DNA from map units 0.3 to 0.65 and HSV-1 (17) DNA from map units 0 to 0.3 and from 0.65 to 1.0. Individual intertypic recombinants will then be tested for their capacity to spread from cornea to trigeminal gaglion in order to correlate neurovirulence with a patricular segment of HSV-1 (17) DNA. Once the area of the chromosome involved in neurovirulence has been located to a particular segment of HSV-1 (17) DNA, additional intertypic recombinants will be generated by marker rescue of HSV-2 (186) DNA with specific HSV-1 (17) DNA restruction endonuclease fragments. This will produce recombinants with smaller regions of HSV-1 (17) DNA inserted into the genome of HSV-2 (186) then will mix infection with both parental strains. Recombinants will then be tested in vivo for neurovirulence following corneal inoculation in order to fine map the physical location of genes responsbile for virus spread from cornea to trigeminal gaglion.